Technical Field
The present invention relates to an engagement device which switches between engagement and disengagement of an engagement element and an engaged element, and to an automatic transmission which has the engagement device.
Related Art
Art related to an engagement device that switches between engagement and disengagement of an engagement element and an engaged element is disclosed in various documents. The engagement device is a self-synchronous shifting clutch (SSS clutch). A switching sleeve rotates at a number of rotations of a vapor turbine until a synchronization number of rotations is reached, and, when the synchronization number of rotations is reached, the switching sleeve is firmly held by a hook in a switching section of a power generator shaft. When the synchronization number of rotations is to be exceeded, the switching sleeve is moved along an axial direction in the direction of the vapor turbine by a screw. After a short time thereof, engagement between a tooth of the switching sleeve and a tooth of the power generator shaft is caused, and torque is transmitted via these teeth. On the other hand, when the number of rotations of the vapor turbine is reduced to a number less than the synchronization number of rotations, the switching sleeve is caused to move along the axial direction in a direction opposite from the vapor turbine by the screw, and the tooth of the switching sleeve and the tooth of the power generator shaft are disengaged from each other, so that the transmission of the torque is discontinued.
In the engagement device described above (SSS clutch), the tooth of the switching sleeve and the tooth of the power generator shaft are engaged to each other by a drive torque from a drive source (vapor turbine). However, when the drive source stops generating the drive torque in an engaged state, the switching sleeve is caused to move along the axial direction in the direction opposite from the vapor turbine by a resistive torque of the drive source, and, consequently, the tooth of the switching sleeve and the tooth of the power generator shaft are disengaged from each other and it becomes impossible to maintain the engaged state. Then, when the drive source again generates the drive torque, the switching sleeve is caused to move along the axial direction in the direction of the vapor turbine, but the transmission of torque is discontinued until the tooth of the switching sleeve and the tooth of the power generator shaft are engaged with each other.